Bacillus thuringiensis (B.t.) produces an insect toxin designated as .delta.-endotoxin It is synthesized by the B.t. sporulating cell. The toxin, upon being ingested in its crystalline form by susceptible insect larvae, is transformed into biologically active moieties by the insect gut juice proteases. The primary target is insect cells of the gut epithelium which are rapidly destroyed.
The reported activity spectrum of B.t. covers insect species within the order Lepidoptera, many of which are major pests in agriculture and forestry. The activity spectrum also includes the insect order Diptera, which includes mosquitos and black flies. See Couch T.L. (1980) "Mosquito Pathogenicity of Bacillus thuringiensis var. israelensis," Developments in Industrial Microbiology 22:61-67, Beegle, C.C., (1978) "Use of Entomogenous Bacteria in Agroecosystems," Developments in Industrial Microbiology 20:97-104. Krieg, et al., Z. ang. Ent. (1983) 96:500-508, describe a B.t isolate named Bacillus thuringiensis var. tenebrionis, which is reportedly active against two beetles in the order Coleoptera These are the Colorado potato beetle, Leptinotarsa decemlineata, and Agelastica alni.
In European Patent Application 0 202 739 there is disclosed a novel B.t. isolate active against Coleoptera. It is known as B. thuringiensis var. san diego (B.t.sd.).
Coleopteran-active strains, such as B.t.sd., can be used to control foliar-feeding beetles The Colorado potato beetle (Leptinotarsa decemlineata), for example, is susceptible to the delta-endotoxin of B.t.sd. and larvae are killed upon ingesting a sufficient dose of spore/crystal preparation on treated foliage.
A number of crops are attacked by flea beetles. These beetles belong to the family Chrysomelidae, the decemlineata. The adults can cause extensive damage by feeding on the foliage.